The invention relates generally to the field of digital computer systems and more particularly to a digital data storage subsystem including a directory for efficiently providing formatting information for records stored by the digital data storage subsystem.
In modem xe2x80x9centerprisexe2x80x9d computing environments, that is, computer systems for use in an office environment in a company, a number of personal computers, workstations, mini-computers and mainframe computers, along with other devices such as large mass storage subsystems, network printers and interfaces to the public telephony system, may be interconnected to provide an integrated environment in which information may be shared among users in the company. Typically, users may be performing a variety of operations, including order receipt, manufacturing, shipping, billing, inventory control, and other operations, in which sharing of data on a real-time basis may provide a significant advantage over, for example, maintaining separate records and attempting to later reconcile them. The users may operate on their own data, which they may maintain on the computers they are using, or alternatively they may share data through the large mass storage subsystems.
One such large mass storage subsystem is described in, for example, U.S. Pat. No. 5,206,939, entitled System And Method For Disk Mapping And Data Retrieval, issued Apr. 27, 1993 to Moshe Yanai, et al (hereinafter, xe2x80x9cthe ""939 patentxe2x80x9d), and U.S. patent application Ser. No. 07/893,509 filed Jun. 4, 1992, in the name of Moshe Yanai, et al., entitled xe2x80x9cSystem And Method For Dynamically Controlling Cache Management,xe2x80x9d now U.S. Pat. No. 5,381,539, issued Jan. 10, 1995, (hereinafter, xe2x80x9cthe ""539 patentxe2x80x9d) both of which are assigned to the assignee of the present invention and incorporated herein by reference. That patent and those applications generally describe an arrangement which allows data, as used by computers, organized in records, with each record being in well-known xe2x80x9cCKDxe2x80x9d (xe2x80x9ccount-key-dataxe2x80x9d) format, to be stored in storage devices which provide a xe2x80x9cfixed blockxe2x80x9d storage architecture. In this arrangement, a large cache is used to buffer data that is transferred from the storage devices for use by the respective computers, and, if the data has been modified, transferred back from to the storage devices for storage.
In the systems described in the aforementioned patent and patent applications, a directory table is used to provide information concerning the data that is stored in the mass storage subsystem. In one embodiment, in which the mass storage subsystem stores data on a number disk storage devices, the table includes information concerning selected characteristics of each of the CKD records stored in the mass storage subsystem, organized by device, cylinder and read/write head or track, and includes such information as record size and certain formatting characteristics. The amount of data that can be stored by individual storage devices is continually increasing over time, both in terms of the number of cylinders that each device can store and in the amount of data each track can store, and so the amount of information which such tables needs to store can become quite large. U.S. patent application Ser. No. 08/790,642, filed: Jan. 29, 1997, in the name of Natan Vishlitzky, and entitled xe2x80x9cDigital Data Storage Subsystem Including Directory For Efficiently Providing Formatting Information For Stored Records,xe2x80x9d now U.S. Pat. No. 6,029,229, issued Feb. 22, 2000, assigned to the assignee of the present invention and incorporated herein by reference, describes a directory table in which the amount of information required for the various records can be advantageously reduced; however, it would be helpful to further reduce the size of the directory table.
The invention provides a new and improved digital data storage subsystem including a directory for efficiently providing formatting information for records stored by the digital data storage subsystem.
In brief summary, the invention provides a digital data storage system comprising a plurality of storage elements, a memory and a control device. The storage elements are configured to retrievably store a series of records. The memory is configured to store a descriptor, the descriptor having associated with each of said records a check value. The control device is configured to, in connection with retrieval of one of said records from said storage element, use the check value associated with the one of said records in connection with verification that the one of said records actually constitutes the record that is to be retrieved.
In one embodiment, the digital data storage system is in the form of a mass storage subsystem in which information is stored on one or more disk storage units, with a storage element constituting a track on a disk storage device and each track storing a plurality of records. Each track in each disk storage device of the digital data storage system is associated with a descriptor. In that embodiment, when the control device retrieves the contents of a record, it can process the contents to generate a check value and compare the generated check value with the check value for the record as stored in the descriptor associated with the track. If they compare appropriately, the control device can determine that the record that was retrieved was, in fact, the record that was to be retrieved. On the other hand, if they do not compare appropriately, the control device can determine that the record that was retrieved was not the proper record. If the contents of the record are updated, the control device can update the check value in the descriptor to reflect the update of the record.